The invention pertains to a hydraulic slide valve control for working cylinders.
Hydraulic working cylinders are primarily used in mechanical engineering for the conveyance of kinetic energy in two opposite directions. This allows the back-and-forth motion of movable parts. The kinetic energy of such a hydraulic drive depends on the volume stream of the hydraulic medium that is directed to the respective side of the piston in the hydraulic cylinder. While in general the piston develops an essentially uniform speed in the back-and-forth travel in the hydraulic working cylinder, the invention provides that the piston is propelled over at least one of its paths at varying speeds. This satisfies practical requirements putting varying demands on the hydraulic drive. For example, it may be important to start the motion at a slow speed, then accelerate it in the medium range, and to slow it down again at the end of the motion. Another requirement consists of starting the motion at a high speed, slowing it down toward midrange and, if so required, bring it to a short halt, and then to accelerate it again at the end. These are only examples. In actual application a multitude of other combinations of motion courses may be required, for which in freely selectable sequence, the piston must be accelerated and delayed.
Such hydraulic working cylinders are known in principle. One of the known design forms provides for a volume control of the hydraulic volume stream, that corresponds to the respective piston speed in the working cylinder, through the hydraulic pressure generator. This requires as a rule volume adjustable pumps where, e.g., for a variable axial piston pump, the slope of the control level determines the respective volume stream. Such pumps are relatively costly. Furthermore, it is not always possible to provide such controlled pumps for the working cylinder. If such pumps are necessary in a control loop from which the control loop of the hydraulic working cylinder branches off, one may often not be able to directly realize varying piston speeds.